Actually, with the last tape deck I bought it was quite difficult to tell the difference between playing a CD and the version I'd made (for playing in the car). This was easy to check as it was a 3 head system so you could toggle between CD and the Tape deck to compare.... and that was with standard iron oxide tapes!
Mind you, probably after playing that tape in the car a few times the quality would have deterioated, but at least on the first play etc it was really impressive.
Unfortunately, it stayed in Aus when I moved over to Europe.